Regulated gene expression is essential to the normal growth and development of cells. The disruption in the network that controls this complex process is correlated with a range of human cancers. Often at the heart of these diseases are malfunctioning transcriptional activators, proteins that associate with specific genes and turn them on such that the proteins they encode are produced. This represents an opportunity to develop therapies that address transcriptional misregulation by identifying molecules that directly inhibit the function of transcriptional activators associated with breast cancer. Two complementary approaches will be used to identify small (drug-like) molecules that inhibit the function of two transcriptional activators, ESX and NF- kappaB (p50/p65 heterodimer) implicated in approximately 30% of breast cancers. Through a combination of in vitro and in vivo studies, these molecules will be assessed as individually and in combination for effectiveness in blocking growth and metastasis of ErbB2(Her2)-positive breast cancer and to provide a detailed understanding of their mechanism of action. From a broader perspective, the transcriptional inhibitors identified in this study will be outstanding tools for dissecting the relationship between misregulated transcription and breast cancer. Our study of these molecules will also be used to build a profile of what characteristics (potency, efficacy, specificity) of an effective transcriptional inhibitor should exhibit. In this way, the molecules identified here will be prototype transcription- targeted therapeutics, opening new avenues for future therapeutic investigations.